This invention relates to multi-cell regenerative photovoltaic photoelectrochemical (RPEC) devices, materials and methods used for internal electrically conductive connections (here called xe2x80x98interconnectsxe2x80x99) for such devices, and materials and methods used for dividing electrically conducting layers within such devices.
Examples of the RPEC cells of the type concerned are disclosed in the following US patents:
4,927,721, Photoelectrochemical cell; Michael Graetzel and Paul Liska, 1990.
5,350,644, Photovoltaic cells; Michael Graetzel, Mohamnmad K Nazeeruddin and Brian O""Regan, 1994.
5,525,440, Method of manufacture of photo-electrochemical cell and a cell made by this muethod; Andreas Kay, Michael Graetzel and Brian O""Regan, 1996.
5,728,487, Photoelectrochemical cell and electrolyte for this cell; Michael Graetzel, Yordan Athanassov and Pierre Bonhote, 1998.
Photoelectrochemical PV cells, as of the type disclosed in the above patents, are capable of being fabricated in a laminate arrangement between two large area substrates without undue expense. A typical arrangement utilises electrically conducting coatings upon the internal surfaces of such substrates, with at least one of such substrates being transparent to visible light (eg. comprised of glass or plastics) and coated with a transparent electron conductor (TEC). However, such TEC coatings, which usually comprise a metal oxide(s), have high resistivity when compared with normal metal conductors, resulting in high resistive losses for large area RPEC cells. In addition, individual RPEC cells generate a voltage that is inadequate for many applications. A multiple of RPEC cells (here called xe2x80x98RPEC modulesxe2x80x99) connected in series would generate higher voltages and minimise total current, thereby minimising power loss due to the resistance of such TEC coating(s). External series connection of RPEC cells can increase manufacturing costs and introduce additional resistive losses. To enable internal series connection of adjacent RPEC cells, selected areas of such conducting coatings must be electrically isolated, portions of such areas overlapped when laminated, interconnects used to connect such overlapped areas and electrolyte-impermeable barriers used to separate the electrolyte of individual cells.
Preferably, the present invention provides materials and methods for interconnects for use with RPEC modules that will overcome the mentioned disadvantages in the art
The present invention provides a regenerative photovoltaic photoelectrochemical device comprising two or more photoelectrochemical cells laminated between two substrates (1,12), with opposing electrical conductors (2,11) supported upon the internal surfaces of said substrates, wherein at least one conductor and it""s adjacent substrate is substantially transparent to visible light, and wherein said conductors on each substrate are each divided into electrically isolated regions with each said cell being formed between parts of two regions of said opposing planar conductors and with each said cell comprising; a photoanode (3) a cathode (11) and an electrolyte medium (5), located between said photoanode and said cathode, where said adjacent photoelectrochemical cells are electrically interconnected in series by an electrically interconnecting material comprising conductive particles (6).
Note that interconnects for use with RPEC modules preferably need not have conductivities approaching that of metals, because the interconnection is made along the entire length of each cell and, moreover, the conduction path length is normally only 30 xcexcm-50 xcexcm, which is the distance between opposing electrically conducting coatings. Thus we have found that efficient and satisfactory RPEC modules can be made with interconnects having bulk resistivity below 20 ohm cm.
In one embodiment, this invention involves the use of an improved composite material as such interconnects which can be deposited as a thin strip of liquid or paste, so that such a strip is adapted to bridge such overlapped areas of conducting coatings and then cured (e.g. crosslinked), thermoset, dried, sintered or otherwise processed to form an electronic conductor between such conducting coatings after such opposing substrates have been assembled. Whilst said composite material can be deposited by conventional screen or stencil printing, this process may cause damage to electrodes previously deposited. In one preferred embodiment of the invention, the composite material is deposited as a thin strip of liquid or paste from a nozzle, whereby said nozzle or substrate or both are moved to effect such deposition. The composite material preferably comprises electrically conducting particles embedded in a polymeric matrix. In a preferred embodiment of the invention, the relative proportion by volume of conductive particles to matrix material in said interconnects is preferably between 1:5 and 2:1, with the high concentrations of conductive particles being preferred.
In one preferred embodiment of the invention, said interconnect may be substantially impervious to and unreactive towards the electrolyte of the RPEC cells, thereby also performing the function of an electrolyte-impermeable barrier. In another preferred embodiment of the invention, the interconnect may be unreactive towards, but not substantially impervious to, the electrolyte of the RPEC cells In this preferred embodiment of the invention, an electrolyte-impermeable barrier located beside the interconnect is used to separate the electrolyte of individual cells. In this preferred embodiment of the invention, said conductive particles and said polymer matrix of said interconnect may be selected from a wider range of materials due to less stringent chemical permeability requirements. In another preferred embodiment of the invention, the interconnect is chemically isolated from the electrolyte of the RPEC cells by electrolyte-impermeable barriers on both sides of the interconnect. In this preferred embodiment of the invention, said conductive particles and said polymer matrix of said interconnect may be selected from a wider range of materials due to less stringent chemical reactivity requirements. Said impermeable barriers may be electrically conducting or non-conducting and may be composed of any suitable material, including, but not limited to, silicones, epoxies, polyesters, polyolefins, acrylic, ormocers and thermoplastics. Said impermeable barriers may be deposited as thin strips of liquid or paste. It is preferable that said impermeable barriers are co-deposited with said interconnect from separate nozzles mounted beside the nozzle from which said interconnect is deposited. In another preferred embodiment of the invention, the interconnect comprises said composite material with a very thin strip of conductive polymer located between said composite material and one or both said conducting coatings. In this preferred embodiment of the invention, said very thin strip(s) of conductive polymer provides improved electrical conductivity between said composite material and said conducting coating(s). In this preferred embodiment of the invention, said very thin strip(s) of conductive polymer may contain polypyrroles, polyanalines, 3,4-ethylene dioxythiophenes and the like and is preferably deposited from a nozzle as previously described.
The polymeric matrix of the interconnect may be electrically conducting (e.g containing polypyrroles, polyanalines, 3,4-ethylene dioxythiophenes and the like) or may be electrically insulating (e.g. containing silicones, epoxies, polyesters, polyolefins, acrylics, ormocers, thermoplastics). Suitable materials for conducting particles may include but are not limited to metallic conductors such as metallic materials (e.g. tungsten, titanium and platinum) in the form of particles and/or metallic beads, and non-metallic conductors such as carbon, ceramics (e.g. indium tin oxide, ruthenium dioxide, cadmium stannate and fluorine-doped stannic oxide), and conducting polymers (e.g. polypyrroles, polyanalines, 3,4-ethylene dioxythiophenes and the like, which can be formed as particles from solution or formed in bulk and commuted to size).
In one preferred embodiment of the invention, the conducting particles are of dimensions approximating the distance between the opposing electrically conducting coatings. In another preferred embodiment of the invention, the conducting particles are of dimensions smaller than said distance and are preferably of dimensions less than 5% of said distance. In still another preferred embodiment of the invention, the conducting particles are of a mixture of sizes, whereby some said particles are of dimensions approximating said distance and other said particles are of dimensions smaller than said distance and are preferably of dimensions less than 5% of said distance. In still another preferred embodiment of the invention, the conducting particles are of a mixture of sizes, whereby some said particles, comprising at least 20% of the total weight of such particles, are of dimensions approximating said distance and other said particles are of dimensions smaller than said distance and are preferably of dimensions less than 5% of said distance. In still another preferred embodiment of the invention, the conducting particles are of a mixture of sizes, whereby some said particles are of dimensions approximating said distance and other said particles, comprising at least 20% of the total weight of such particles, are of dimensions smaller than said distance and are preferably of dimensions less than 5% of said distance. In still another preferred embodiment of the invention, the conducting particles are of a mixture of sizes, whereby some said particles are of dimensions approximating said distance, other said particles are of dimensions smaller than said distance and are preferably of dimensions less than 5% of said distance, and still other said particles are of dimensions less than said distance and greater than 5% of said distance. Certain mechanical forces, such as wind loading, may cause a short circuit to occur between the laminated electrodes in some RPEC module designs. It is a feature of this invention, that interconnects containing conductive particles of dimensions approximating to or near to said distance between said opposing electrically conducting coatings may prevent or minimise the occurrence of such short circuits during such mechanical loading.